CA2428892A1 - Very high frequency oscillatory ventilator - Google Patents
Very high frequency oscillatory ventilator Download PDFInfo
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- CA2428892A1 CA2428892A1 CA 2428892 CA2428892A CA2428892A1 CA 2428892 A1 CA2428892 A1 CA 2428892A1 CA 2428892 CA2428892 CA 2428892 CA 2428892 A CA2428892 A CA 2428892A CA 2428892 A1 CA2428892 A1 CA 2428892A1
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- ventilation
- high frequency
- frequency oscillatory
- oscillatory
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- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61M—DEVICES FOR INTRODUCING MEDIA INTO, OR ONTO, THE BODY; DEVICES FOR TRANSDUCING BODY MEDIA OR FOR TAKING MEDIA FROM THE BODY; DEVICES FOR PRODUCING OR ENDING SLEEP OR STUPOR
- A61M16/00—Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes
- A61M16/0096—High frequency jet ventilation
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Abstract
A system for administering oscillatory ventilation at a rate of 60 Hz and a very high frequency oscillatory ventilator consisting of a modified 60 Hz line-operated vaccum pump and a rotameter controlled oxygen bias flow regulator.
Description
VERY HIGH FREQUENCY OSCILLATORY VENTILATOR
FIELD OF THE INVENTION
This invention relates to a very high frequency oscillatory ventilator.
BACKGROUND OF THE INVENTION
Ventilators have many uses in the medical field and are used to treat different medical conditions.
For example, ventilators have been used to treat Acute Respiratory Distress Syndrome CARDS) for many years both with respect to adults and with respect to children. Conventional ventilators operate at a rate of 15 Hz.
Considerable effort has been directed to produce a high frequency oscillatory ventilator which is both effective and less injurious for the patient.
Uncertainty existed for many years with respect tc~ the efficacy of high frequency oscillatory ventilation as compared with those of conventional ventilation for the respiratory support of very preterm infants. Various studies have been conducted indicating that high frequency oscillatory ventilation works well in the treatment of very preterm infants. Other studies have established significant benefit of using high frequency oscillatory ventilation in terms of the pulmonary outcome for very low birth weight infants without an increase in the occurrence of other complications of premature birth.
Pulmonary disease, principally due to the respiratory distress syndrome (RDS) continues to be a major cause of mortality and morbidity in neonates despite the increased use of antenatal steroiods and surfactant replacement therapy. It has been found that high frequency oscillatory ventilation is an effective method of providing ventilation and oxygenation in severe experimental pulmonary disease and may result in less lung injury.
A vast majority of patients who are admitted to intensive care units of hospitals will need artificial ventilation. The usual means through whicl this is achieved will be via positive pressure ventilation wherein gas is delivered under positive pressure, allowing alveoli expansion and gas exchange.
However, the effects of this non-physiological approach to ventilation are numerous and can be detrimental. Furthermore, in diseased lungs positive pressure ventilation may not always provide adequate C02 clearance or oxygen delivery and may even result in alveolar/lung damage due to ventilating at high airway pressures.
An alternate approach to conventional ventilation has emerged over the last decade and is known as High Frequency Ventilation.
Along with patients suffering with respiratory failure, there are certain patients who need ventilatory support for other medical reasons. Post operative ICU
admissions for waking, warming and weaning are not uncommon and certain maxillofacial surgical patients require a period of post operative care and management on ICU during which time the patient is kept sedated and ventilated.
Once a patient has been identified as needing artificial ventilation, they are intubated and placed on a ventilator and ventilated using positive pressure.
Gases are delivered to the patient using pressure to inflate the lungs, expand the alveoli and allow for gas exchange and oxygenation.
It is thought that patients who are at risk of further lung damage due to increase in airway pressure secondary to increases in resistance anal decreases in compliance, may benefit from HFOV. When conventional ventilation fails to safely and adequately provide respiratory support, HFOV can be considered an alternative.
Essentially, HFOV provides small tidal volumes usually equal to, or less than, the dead space; 150 millilitres, at a very fast rate (Hertz-Hz) of between 4-5 breaths per second. The delivery of tidal volumes of dead space or less at very high frequencies enables the maintenance of a minute volume. Lungs are kept open to a constant airway pressure via a mean pressure adjust system. Further, HFOV allows for the decoupling of oxygenation from ventilation: it allows the clinician to separately adjust either oxygenation or ventilation.
The core of an HFOV system is a piston assembly. A typical system incorporates an electronic circuit, or square-waive driver, which powers a linear drive motor. This motor consists of an electrical coil within a magnet, similar to a permanent magnet speaker. When a positive polarity is applied to the square-'nave driver, the coil is driven forward. The coil is attached to a rubber bellows, or diaphragm, to create a piston. When the coil moves forward, the piston moves toward the patient airway, creating the inspiratory phase. When the polarity becomes negative, the electrical coil and the attached piston are driven away from the patient, creating an active expiration.
The amount of polarity voltage applied to the electrical coil detemnines the distance that the piston is driven toward/away from the patient' s airway. Therefore increasing the polarity voltage increases the piston movement, or amplitude. The easiest way to conceptualise this polarity voltage, or amplitude, is to view it as the means by which tidal volumes are delivered, the greater the piston displacement (amplitude) the more volume delivered to the patient. It is the piston displacement which causes the oscillations. The extent to which the amplitude increases depends on the resistence the piston encounters to forward movement. For example, when the oscillator is used with a patient with low compliance or high resistance, the piston meets greater pressure during the inspiratory phase.
Since tidal volumes are so low, gas transport mechanisms other than conventional bulk flow must be invoked to explain gas and X02 flow.
Along with the above mentioned amplitude which ,provides ventilatory volumes, a Mean Pressure Adjust control knob allows for adjustments in mean airway pressure (Paw) . This control varies the resistance placed on a mushroom shaped control valve on the patient circuit at the terminus of the expiratory limb. This allows the clinician to manipulate the Paw. Adjusting the Paw enables lung recruitment, keeps lungs and alveoli open at a consent pressure, thus avoiding lung expansion/collapse, lung expansion/collapse which is detrimental to the lungs. Research has also shown that increasing the Paw during HFOV does not effect cardiac out put, unlike conventional ventilation, and increases oxygenation . The mean pressure adjust control is Bias Flow dependent. Bias flow is the rate at which the flow of gas, through the oscillator, is delivered to the patient.
The speed at which the oscillator runs is set by manipulating the frequency.
The frequency control sets the breaths per minute in Hertz (H~:). One Hz is equal to one breath per second, i.e., 60 breaths per minute. A frequency of 5 Hz gives a frequency of 5 breaths per second, or 300 breaths per minute. An important point to remember is that as frequency is increased, the excursion of the piston is limited by the time allocated for each breath cycle. Thus, changes in frequency will effect lPaw and the amplitude.
In conjunction with amplitude, mean airway adjust , bias flow, and frequency control, an oscillator will usually also allow for the inspiratory time to be adjusted. The inspiratory time will be displayed as % Inspiratory Time. Further, as with conventional ventilators, alarm limits can also be set.
The advantages of using HFOV are: smaller tidal volumes, a constant, less variable, airway pressure and the fact that nonbulk-flow mechanisms may improve V/Q
matching. HFOV is used to avoid conventionally ventilating atelectasis prone lungs in ARDS. Over distention of the lungs and ongoing atelectasis cont~°ibute to progressive lung injury which arises not d'arectly from the disease process itself, but from the impact of the ventilator patterns used to support gas exchange during the course of the illness by conventional ventilation. Atelectasis can be halted, and even reversed, during HFOV, while avoiding the over distention so commonly seen with conventional ventilation.
Thus, HFOV is used to minimize ventilator-related lung injuries in AkDS. The protective strategy of a constant airway pressure, with smaller tidal pressure swings, preventing over distention, are reasons why HFOV is used.
SUMMARY OF THE INVENTION
To at least partially overcome the disadvantages, the present invention provides a ventilation modality that is the most effective but least injurious for the patient.
In one embodiment of this invention, a system has been developed for administering oscillatory ventilation at a rate of 60 Hz.
To this end, high frequency ventilators have been developed which use very rapid but extremely small breaths thereby reducing injury to the lungs. As such, much interest has been expressed in high frequency oscillatory ventilators for treatment of neonates and pediatrics as well as in the adult population.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic view of the very high frequency oscillator pump used in the present invention.
Figure 2 is a schematic view of the setup of the very high frequency oscillator setup.
DESCRIPTION
The search for a ventilation modality that is the rn~ost effect but least injurious for the patient has resulted in the development of high frequency oscillatory ventilation (HFOV).
A system has been developed for administering oscillatory ventilation at a rate of 60Hz which is four times higher than the traditional 15 Hz.
To test the very high frequency oscillatory ventilation, the following experiment was conducted. The very high frequency oscillatory ventilation (VHFOV) was tested on rats for safety and efficacy.
After induction with I~etamine-Xylazine, the rat was placed on a heating pad, tracheostomised with a l4Ga. Blunt needle and its carotid artery was catheterised for arterial pressure monitoring and blood-gas sampling. After five minutes of spontaneous ventilation and data gathering, the rat was connected to a VHFO ventilator consisting of a modified 60 Hz line-operated vacuum pump (Medo, Mod.35002) and a rotameter controlled oxygen bias flow regulator. The rat was paralysed by IM
administration of Pancuronium as necessary. The amplitude of oscillations was previously estimated by the width of the smeared video-microscopic image of a chest hair with the displacement of the same hair in response to a known inspiratory volume. After two hours of VHFOV, the rat was sacrificed and the lungs removed for subsequent analysis.
All the rats survived 2 hours of ventilation with VHFO with pH, p02, pC02, BP, HR, Sp02 in the normal range. The estimated tidal volume of the oscillations was 1 ml/kg. Comparison of the lungs ventilated with VHFO to unventilated controls indicated little or no differences on microscopic examination.
Those skilled in the art will recognize or be able to ascerl:ain using no more than routine experimentation, many equivalents to the specific embodiments described herein.
Such equivalents are intended to be encompassed by the following claims.
FIELD OF THE INVENTION
This invention relates to a very high frequency oscillatory ventilator.
BACKGROUND OF THE INVENTION
Ventilators have many uses in the medical field and are used to treat different medical conditions.
For example, ventilators have been used to treat Acute Respiratory Distress Syndrome CARDS) for many years both with respect to adults and with respect to children. Conventional ventilators operate at a rate of 15 Hz.
Considerable effort has been directed to produce a high frequency oscillatory ventilator which is both effective and less injurious for the patient.
Uncertainty existed for many years with respect tc~ the efficacy of high frequency oscillatory ventilation as compared with those of conventional ventilation for the respiratory support of very preterm infants. Various studies have been conducted indicating that high frequency oscillatory ventilation works well in the treatment of very preterm infants. Other studies have established significant benefit of using high frequency oscillatory ventilation in terms of the pulmonary outcome for very low birth weight infants without an increase in the occurrence of other complications of premature birth.
Pulmonary disease, principally due to the respiratory distress syndrome (RDS) continues to be a major cause of mortality and morbidity in neonates despite the increased use of antenatal steroiods and surfactant replacement therapy. It has been found that high frequency oscillatory ventilation is an effective method of providing ventilation and oxygenation in severe experimental pulmonary disease and may result in less lung injury.
A vast majority of patients who are admitted to intensive care units of hospitals will need artificial ventilation. The usual means through whicl this is achieved will be via positive pressure ventilation wherein gas is delivered under positive pressure, allowing alveoli expansion and gas exchange.
However, the effects of this non-physiological approach to ventilation are numerous and can be detrimental. Furthermore, in diseased lungs positive pressure ventilation may not always provide adequate C02 clearance or oxygen delivery and may even result in alveolar/lung damage due to ventilating at high airway pressures.
An alternate approach to conventional ventilation has emerged over the last decade and is known as High Frequency Ventilation.
Along with patients suffering with respiratory failure, there are certain patients who need ventilatory support for other medical reasons. Post operative ICU
admissions for waking, warming and weaning are not uncommon and certain maxillofacial surgical patients require a period of post operative care and management on ICU during which time the patient is kept sedated and ventilated.
Once a patient has been identified as needing artificial ventilation, they are intubated and placed on a ventilator and ventilated using positive pressure.
Gases are delivered to the patient using pressure to inflate the lungs, expand the alveoli and allow for gas exchange and oxygenation.
It is thought that patients who are at risk of further lung damage due to increase in airway pressure secondary to increases in resistance anal decreases in compliance, may benefit from HFOV. When conventional ventilation fails to safely and adequately provide respiratory support, HFOV can be considered an alternative.
Essentially, HFOV provides small tidal volumes usually equal to, or less than, the dead space; 150 millilitres, at a very fast rate (Hertz-Hz) of between 4-5 breaths per second. The delivery of tidal volumes of dead space or less at very high frequencies enables the maintenance of a minute volume. Lungs are kept open to a constant airway pressure via a mean pressure adjust system. Further, HFOV allows for the decoupling of oxygenation from ventilation: it allows the clinician to separately adjust either oxygenation or ventilation.
The core of an HFOV system is a piston assembly. A typical system incorporates an electronic circuit, or square-waive driver, which powers a linear drive motor. This motor consists of an electrical coil within a magnet, similar to a permanent magnet speaker. When a positive polarity is applied to the square-'nave driver, the coil is driven forward. The coil is attached to a rubber bellows, or diaphragm, to create a piston. When the coil moves forward, the piston moves toward the patient airway, creating the inspiratory phase. When the polarity becomes negative, the electrical coil and the attached piston are driven away from the patient, creating an active expiration.
The amount of polarity voltage applied to the electrical coil detemnines the distance that the piston is driven toward/away from the patient' s airway. Therefore increasing the polarity voltage increases the piston movement, or amplitude. The easiest way to conceptualise this polarity voltage, or amplitude, is to view it as the means by which tidal volumes are delivered, the greater the piston displacement (amplitude) the more volume delivered to the patient. It is the piston displacement which causes the oscillations. The extent to which the amplitude increases depends on the resistence the piston encounters to forward movement. For example, when the oscillator is used with a patient with low compliance or high resistance, the piston meets greater pressure during the inspiratory phase.
Since tidal volumes are so low, gas transport mechanisms other than conventional bulk flow must be invoked to explain gas and X02 flow.
Along with the above mentioned amplitude which ,provides ventilatory volumes, a Mean Pressure Adjust control knob allows for adjustments in mean airway pressure (Paw) . This control varies the resistance placed on a mushroom shaped control valve on the patient circuit at the terminus of the expiratory limb. This allows the clinician to manipulate the Paw. Adjusting the Paw enables lung recruitment, keeps lungs and alveoli open at a consent pressure, thus avoiding lung expansion/collapse, lung expansion/collapse which is detrimental to the lungs. Research has also shown that increasing the Paw during HFOV does not effect cardiac out put, unlike conventional ventilation, and increases oxygenation . The mean pressure adjust control is Bias Flow dependent. Bias flow is the rate at which the flow of gas, through the oscillator, is delivered to the patient.
The speed at which the oscillator runs is set by manipulating the frequency.
The frequency control sets the breaths per minute in Hertz (H~:). One Hz is equal to one breath per second, i.e., 60 breaths per minute. A frequency of 5 Hz gives a frequency of 5 breaths per second, or 300 breaths per minute. An important point to remember is that as frequency is increased, the excursion of the piston is limited by the time allocated for each breath cycle. Thus, changes in frequency will effect lPaw and the amplitude.
In conjunction with amplitude, mean airway adjust , bias flow, and frequency control, an oscillator will usually also allow for the inspiratory time to be adjusted. The inspiratory time will be displayed as % Inspiratory Time. Further, as with conventional ventilators, alarm limits can also be set.
The advantages of using HFOV are: smaller tidal volumes, a constant, less variable, airway pressure and the fact that nonbulk-flow mechanisms may improve V/Q
matching. HFOV is used to avoid conventionally ventilating atelectasis prone lungs in ARDS. Over distention of the lungs and ongoing atelectasis cont~°ibute to progressive lung injury which arises not d'arectly from the disease process itself, but from the impact of the ventilator patterns used to support gas exchange during the course of the illness by conventional ventilation. Atelectasis can be halted, and even reversed, during HFOV, while avoiding the over distention so commonly seen with conventional ventilation.
Thus, HFOV is used to minimize ventilator-related lung injuries in AkDS. The protective strategy of a constant airway pressure, with smaller tidal pressure swings, preventing over distention, are reasons why HFOV is used.
SUMMARY OF THE INVENTION
To at least partially overcome the disadvantages, the present invention provides a ventilation modality that is the most effective but least injurious for the patient.
In one embodiment of this invention, a system has been developed for administering oscillatory ventilation at a rate of 60 Hz.
To this end, high frequency ventilators have been developed which use very rapid but extremely small breaths thereby reducing injury to the lungs. As such, much interest has been expressed in high frequency oscillatory ventilators for treatment of neonates and pediatrics as well as in the adult population.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a schematic view of the very high frequency oscillator pump used in the present invention.
Figure 2 is a schematic view of the setup of the very high frequency oscillator setup.
DESCRIPTION
The search for a ventilation modality that is the rn~ost effect but least injurious for the patient has resulted in the development of high frequency oscillatory ventilation (HFOV).
A system has been developed for administering oscillatory ventilation at a rate of 60Hz which is four times higher than the traditional 15 Hz.
To test the very high frequency oscillatory ventilation, the following experiment was conducted. The very high frequency oscillatory ventilation (VHFOV) was tested on rats for safety and efficacy.
After induction with I~etamine-Xylazine, the rat was placed on a heating pad, tracheostomised with a l4Ga. Blunt needle and its carotid artery was catheterised for arterial pressure monitoring and blood-gas sampling. After five minutes of spontaneous ventilation and data gathering, the rat was connected to a VHFO ventilator consisting of a modified 60 Hz line-operated vacuum pump (Medo, Mod.35002) and a rotameter controlled oxygen bias flow regulator. The rat was paralysed by IM
administration of Pancuronium as necessary. The amplitude of oscillations was previously estimated by the width of the smeared video-microscopic image of a chest hair with the displacement of the same hair in response to a known inspiratory volume. After two hours of VHFOV, the rat was sacrificed and the lungs removed for subsequent analysis.
All the rats survived 2 hours of ventilation with VHFO with pH, p02, pC02, BP, HR, Sp02 in the normal range. The estimated tidal volume of the oscillations was 1 ml/kg. Comparison of the lungs ventilated with VHFO to unventilated controls indicated little or no differences on microscopic examination.
Those skilled in the art will recognize or be able to ascerl:ain using no more than routine experimentation, many equivalents to the specific embodiments described herein.
Such equivalents are intended to be encompassed by the following claims.
Claims (2)
1. A system for administering oscillatory ventilation at a rate of 60 Hz.
2. A very high frequency oscillatory ventilator consisting of a modified 60 Hz line-operated vaccum pump and a rotameter controlled oxygen bias flow regulator.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2428892 CA2428892A1 (en) | 2003-05-16 | 2003-05-16 | Very high frequency oscillatory ventilator |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2428892 CA2428892A1 (en) | 2003-05-16 | 2003-05-16 | Very high frequency oscillatory ventilator |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2428892A1 true CA2428892A1 (en) | 2004-11-16 |
Family
ID=33437987
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2428892 Abandoned CA2428892A1 (en) | 2003-05-16 | 2003-05-16 | Very high frequency oscillatory ventilator |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2428892A1 (en) |
-
2003
- 2003-05-16 CA CA 2428892 patent/CA2428892A1/en not_active Abandoned
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